If you agree to participate in this study, you will be asked to undergo some screening tests or procedures to confirm that you are eligible. Many of these tests and procedures are likely to be part of regular cancer care and may be done even if it turns out that you do not take part in the research study. If you have had some of these tests or procedures recently, they may or may not have to be repeated. The screening will include the following: a medical history, physical examination, biopsy of your tumor, anal and groin exam, archival tumor tissue, CT or PET-CT, MRI, blood tests and a serum pregnancy test. If these tests show that you are eligible to participate in the research study, you will begin the study treatment. If you do not meet the eligibility criteria, you will not be able to participate in this research study.